When the mind sees something favourable or attractive, it is hard for the mind to forget about it. It gets attached to it. Even if the mind attaches to one thing, if it saw another attractive thing it would be attracted to that too.
It will keep searching and attaching, a continuous cycle of greed. Thirst for more. The mind indeed travels like a thirsty shopper, excited of all the things found in the shopping centre and wanting not something but all. Craving for more is the state of this mind, full of pure greed.
Real life example:
When I go on ebay, I don’t get 100% satisfied. When I buy something, I would want another thing. This mind which I call ‘myself’ craves for more, despite whatever I have with me. Its nature is greed. Greed is like a fire, it burns us out.